Hybrid material, use of said hybrid material and method for making same

ABSTRACT

The present invention relates to a hybrid material, its use and its production process.  
     The hybrid material comprises a polymer with acid groups. The inorganic part of the said hybrid material is constituted by the combination of at least two metal oxide components, whereof at least one comprises a functional group permitting an interaction and a spatial relationship with the acid groups of the polymer.

[0001] The present invention relates to a hybrid material, its use andits production process.

[0002] Among the fuel cells of greatest interest in applicationsrelating to the motor vehicle or car sector are solid polymerelectrolyte fuel cells.

[0003] In a solid electrolyte fuel cell, the polymer solid electrolyteis a proton exchange membrane. Such membranes must have a lowpermeability to reactant gases (e.g. H₂, CH₄ and O₂) and a maximumelectrical and catalytic efficiency. They must also have adequateconduction properties and a minimum ohmic drop under a high currentdensity.

[0004] Materials which can serve as a basis for such membranes mustmainly have the following chemical and electrochemical properties:stability of the plastic material in a reducing medium, oxidationstability and hydrolysis stability. The membrane must also have a goodhydrothermal stability. The use of perfluorine acid ionomers such ase.g. NAFION® has been proposed as a proton exchange membrane for suchapplications.

[0005] For many membranes the conductivity of the membrane is verysensitive to the degree of hydration. When subject to risingtemperatures and temperatures close to the boiling point of water, dueto the decreasing dehydration of the membrane the problem arises of areduction in its electrical conductivity and at the same time anincrease in the fuel transfer permeability. This leads to a reduction inthe performance characteristics or a deterioration of the membrane.

[0006] However, numerous advantages are associated with the increase inthe operating temperature of a proton exchange membrane fuel cell,namely in the case of stationary applications the cogeneration of heatcan be useful. For use as the motive energy source of a vehicle, such asroad vehicles and more specifically cars, the use of fuel cellsoperating at a higher temperature makes it possible to reduce the heatdissipation capacity of the cooling system and therefore reduce the bulkthereof. A reduction in the bulk facilitates the integration thereof inthe vehicle and decreases the price.

[0007] The object of the present invention is to provide a material fordeveloping thermostable membranes usable in electrochemical devicesoperating at temperatures above 90° C.

[0008] The objective of the present invention is realized by a hybridmaterial comprising a polymer having acid groups. The inorganic part ofsaid acid material is constituted by the combination of at least twometal oxide components, whereof at least one comprises a functionalgroup permitting an interaction and a spatial relationship with the acidgroups of the polymer.

[0009] The hybrid material is in particular a polymer matrix. It ispreferable for the metal oxide components to be of metals of group IVand in particular SiO₂. Without detriment to the general nature of thedescription hereinafter, the explanations are given for SiO₂, but thelatter can be replaced by other metal oxides.

[0010] It can in particular be advantageous to use a polymer hybridmaterial having acid groups. This hybrid material contains a componentwith at least two SiO₂, each molecule of said component being fixeddirectly or indirectly to the polymer material whilst respecting aspatial relationship with respect to an acid group.

[0011] Preferably the acid groups are formed by sulphonic groups. It isalso preferable for the acid polymer material to be an organic polymer.It can in particular be a fluorine-free organic polymer.

[0012] The material can be formed from a polymer such as e.g. asulphonated polysulphone or a sulphonated polyarylether ketone.Sulphonated polyarylether ketone examples are sulphonated polyetherketones such as s-PEK, s-PEEK, s-PEEKK, s-PEKK and S-PEKEKK. An exampleof a polysulphone which can be sulphonated is marketed under the nameUdel®. It is also possible to use other sulphonated polymer materialssuch as a sulphonated polyether sulphone (PES, e.g. sulphonatedVictrex®), a sulphonated polyphenylether sulphone (s-PPSU, e.g.sulphonated Radel®), a sulphonated styrene/ethylene copolymer (s-SES) ora sulphonated styrene/butadiene copolymer (s-SBS, s-SIS, e.g.sulphonated Kraton®).

[0013] The two inorganic components can be formed from precursors havinghydrolyzable functions permitting a copolymerization. One of thesecomponents can be constituted by a metal alkoxide (RO)_(x)M and theother by a functionalized alkoxy silane (R′O)₃SiR″ or (R′O)₂SiR₂″. Thefunctional groups are R″, R and R′ groups, which can be identical ordifferent alkyl groups. The alkoxy groups can be linear, such as primaryalkoxide groups (e.g. methoxy, propoxy) or secondary alkoxide groups(e.g. isopropoxy). It is preferable for the R″ groups to have a basiccharacter. These groups contain alkyl or aryl chains and have a basicfunction, preferably including a nitrogen atom. It is possible to havean amine group. Alternatively, one of the inorganic components can beintroduced in the form of small metal oxide particles. It can be useful,but not essential, for the basic function to be located at one end ofthe R″ group.

[0014] For such a material, it is possible to control its properties byvarying the ratio between the number of acid groups of the polymermaterial and the number of groups having a basic character of theinorganic component. If the number of groups with a basic character issmaller than the number of acid groups of the polymer matrix, the hybridmaterial has free acid groups which can exert a certain function.

[0015] According to another preferred form of the hybrid material, theinorganic component is formed from metal oxide particles having at leastlocally on their surface a basic character. This basic character ispreferably due to basic groups on the surface of the particle. Accordingto a preferred embodiment of the invention the diameter of the metaloxide particles is below 50 nm and is in a particularly preferred mannerequal to or below 10 nm.

[0016] It can e.g. be a silica particle, which is coated with amonomeric layer of molecules having a group with a basic character. Thegroup with a basic character preferably contains a nitrogen atom and canmore particularly be an amine group. An example of molecules able tocoat a silica particle with a monomeric layer is e.g. aminophenyltrimethoxysilane (APTMOS).

[0017] In a hybrid material according to the invention, the spatialrelationship between the polymer matrix and the inorganic part is due toa strong interaction. This strong interaction is more particularlyconstituted by an ionic interaction between the functional group of thepolymer and a functional group of the inorganic part. This ionicinteraction is due to the proton transfer from the acid group of thepolymer to the basic group of the inorganic part. A hybrid materialaccording to the invention preferably has a homogeneous distribution ofthe inorganic part. A beneficial effect for the use of the material asthe membrane of a fuel cell is the fact that the fuel gas transferthrough the membrane is limited. This more particularly applies in thecase of fuel cells operating directly with methanol. This effect isfurther improved if there is a regular distribution of the inorganicpart.

[0018] A material according to the invention can have a metal oxidecontent between 1 and 50 wt. %. The metal oxide content is preferablybetween 6 and 20 wt. % or between 6 and 10 wt. %. The percentages givenrelate to weight measurements and do not relate to molar masspercentages.

[0019] A material according to the invention can also be formed by aninorganic substrate interpenetrated by the polymer, if the metal oxidecontent is relatively high. Then another spatial structure of thematerial is obtained. Thus, the material has an inorganic substrate, thesubstrate being formed by the metal oxide, and the intercalated polymer.

[0020] The intercalating of the polymer in the crude inorganic substratecan take place in the absence of a prior integration of the poroussupport by the ionic polymer. This can be a direct formation of twointercalated spatial structures taking place at the same time.

[0021] Such a hybrid material is more particularly formed if the metaloxide content is between 30 and 60 wt. %. The metal oxide content ismore particularly in the range 40 to 50 wt. %.

[0022] According to the invention it is advantageous if the hybridmaterial comprises a porous inorganic substrate with an ionic conductivepolymer placed within the substrate pores. In the case of the use of thematerial as a conductive membrane, the conductivity through the membraneis mainly dependent on the number of channels or pores permitting an iontransfer, e.g. hydrogen atomic nuclei (protons) through the membrane.The number of channels is more particularly dependent on the metal oxidecontent of the material.

[0023] According to the invention the inorganic substrate of such amaterial is the product of a co-condensation of a metal tetraalkoxideand a functionalized trialkoxy metal oxide. As described hereinbefore,the metal can be constituted by silicon. This co-condensation can moreparticularly take place in the presence of an ionic polymer. This ionicpolymer can in particular belong to the family of ionic conductivepolymers or aromatic ionomers or heterocyclic ionomers.

[0024] The inorganic substrate is preferably porous and can be theproduct of a co-condensation in a tetraalkoxy silane and trialkoxysilane polymer solution functionalized by basic organic groups in thepresence of an ionomer. The ionic polymer can be chosen from amongelements of the group of sulphone, phosphorus or carboxyl ionomers andcan in particular be a sulphonated polyether ketone.

[0025] The basic inorganic groups of the trialkoxy metal (trialkoxysilane) functionalized by said basic group are preferably chosen fromamong alkyl or acrylamino groups. It can more particularly be anaminophenyl trialkoxy silane. An example of an aminophenyl trialkoxysilane is aminophenyl trimethoxy silane (APTMOS). The alkoxy groups canbe chosen from among members of the methoxy, ethoxy and butoxy groups.

[0026] A hybrid material according to the invention is more particularlycharacterized in that the porous inorganic substrate comprises amicro-infrastructure interpenetrated with the ionic conductor. Themicro-infrastructure is more particularly present in the form of pores,the size of the pores being in the range of nanometric structures. Thesize of the pores is preferably between 1 and 10 nm. More particularlythe size of the pores is between 2 and 7.5 nm. It can even be within therange 3 to 6 nm.

[0027] It is also possible to characterize the structure of theinorganic substrate by its specific surface area. The evaluation of thespecific surface area can take place according to the BET method, whichis a standard method for evaluating the surface of porous materials. Oneliminating the organic part by combustion, values are obtained for thesurface between 200 and 120 m²/g⁻¹. Preferably the specific surface areadetermined by the above method is between 300 and 900 m²/g⁻¹.

[0028] The materials formed in accordance with the invention have atransparent, flexible appearance. Most of the materials are relativelymechanically robust.

[0029] A property of hybrid materials having a porous inorganicstructure is the fact that they have an ionic conductivity equal to orvery close to that of the sulphonated polymer of approximately 0.001 toapproximately at least 0.1 Scm⁻¹.

[0030] The manufacture of the membranes and in particular the fixing ofthe membranes of said material to functional supports is made easier ifthe material is present in the form of a solution. A material accordingto the invention can be dissolved in a polar and preferably aproticsolvent. Examples of such solvents are dimethyl formamide (DMF),dimethyl acetamide (DMAc), dimethyl sulphoxide (DMSO) and in particularN-methyl-2-pyrrolidone (NMP).

[0031] The hybrid material according to the invention can be a membrane,preferably a membrane used for cationic transfer and more specificallyit can be used as a membrane in a fuel cell of the PEM type (protonexchange membrane) and also of the DMFC type (direct methane fuel cell).Such membranes can also be used in all other electrolysis andelectrodialysis processes.

[0032] A fuel cell according to the present invention has a membranecomposed of a hybrid material according to the invention. Such a fuelcell can operate directly with methanol as the fuel. The operating pointcan be at temperatures above 90° C., or above 110° C. and even above130° C.

[0033] A process for the production of a hybrid material according tothe invention is characterized in that the acid polymer matrix is mixedwith inorganic components and/or with precursors of said components.Mixing takes place in the presence of at least one solvent. Thesesolvents and/or at least one of their precursors have a functional groupwhich can be fixed to the acid group of the polymer matrix. The fixingand/or formation of the inorganic component takes place in the immediatevicinity of the acid group.

[0034] According to a preferred embodiment of this process, the polymeris dissolved in at least one solvent, dissolving taking place inpreferred manner under an inert gas and more particularly at atemperature of approximately 130° C. An example of an inert gas usablefor dissolving the polymer is nitrogen.

[0035] It can also be advantageous if the inorganic component and/or itsprecursors are dissolved in at least one solvent and for the precursorsof the component to be in the same solution of at least one solvent.

[0036] A preferred embodiment of the process according to the inventionconsists of adding to an acid polymer solution a solution containing adispersion of the metal oxide and/or a solution of precursors of saidcomponents. The mixture can be homogenized.

[0037] The solvent can be an aprotic polar solvent and more specificallyN-methyl-2-pyrrolidone (NMP).

[0038] An advantageous form of the production process for the hybridmaterial is characterized in that the fixing and/or formation of theinorganic part takes place in a sol-gel reaction. It preferably takesplace in the presence of water and an acid, organic or mineral catalyst.

[0039] According to an embodiment of the process according to theinvention one of the precursors of the component can serve as thestarting point for the formation of chains. The formation of chains cane.g. take place by polycondensation. Polycondensation can take placeeither between molecules of the same precursor or between said precursorand another precursor. One of the precursors has a dispersant function,an initiator function of the formation of chains and a function offixing the chain to the polymer material.

[0040] For example, as a result of its basic character, it can e.g.interact with the acid group of the polymer. As a result of thisinteraction, the distribution of said precursor is oriented by thepresence of the acid groups of the polymer. This effect produces adispersion of said component. The hydrolyzable groups of the sameprecursor make it possible to bring about a chain formation reaction.This chain formation reaction more specifically takes place bypolycondensation with other molecules of the same precursor or moleculesof another precursor.

[0041] A process according to the invention can be characterized by theuse of precursors of inorganic components having a basic group.Preferably said basic group contains nitrogen and can more particularlybe an amine group. This basic group interacts with an acid group of thepolymer material. An example of a precursor is aminophenyl trimethoxysilane (APTMOS).

[0042] In a process according to the invention a precursor can betetraethoxy silane (TEOS), which can e.g. be fixed by polycondensationto APTMOS. Oligomeric or polymeric chains with several SiO₂ groups canbe arranged in such a way that SiO₂ networks form. Such a process can beperformed on the basis of a weight ratio between TEOS and APTMOS of atleast 70:30 (i.e. at least 70 wt. % TEOS and at the most 30 wt. %APTMOS) and preferably between 80:20 and 95:5.

[0043] A process according to the invention can be characterized in thatthe inorganic part is a SiO₂ particle having basic groups on itssurface. These basic groups can be located on the surface of theparticle by the condensation of APTMOS molecules with silanol groups ofthe surface of the particles. In such a process it can be preferable forthe weight ratio between the silica and APTMOS particles to be greaterthan 60:40 (i.e. at least 60 wt. % silica and at the most 40 wt. %APTMOS) and more preferably between 80:20 and 95:5. A preferredembodiment of the invention involves a transfer of particles from anaqueous solvent to the organic solvent of the polymer.

[0044] A process according to the invention can involve the formation ofa membrane. The formation of the membrane can more particularly takeplace by a process of pouring the polymer material mixture with theinorganic component and/or the precursors of the component on a support.

[0045] A material according to the invention can also be obtained by theco-condensation of a metal tetraalkoxide (silicon) and functionalizedtrialkoxy metal (trialkoxy silane) in an ionic conductive polymersolution. The formation can take place as a single process. It ispossible for the process to take place directly and in the absence of animpregnation of the organic substrate with an ionic polymer. The ionicconductor is preferably an ionic conductive polymer, aromatic ionomer orheterocyclic ionomer. It is more particularly a sulphone, phosphorus orcarboxyl ionomer. The ionic conductive polymer can thus be chosen fromthe group of sulphone, phosphorus or carboxyl ionomers and is moreparticularly a member of the group of sulphonated polyether ketones.

[0046] The co-condensation of the material more particularly takes placein an aprotic solvent with a high relative dielectric constant of atleast greater than 37 and preferably greater than 45. Theco-condensation of these materials more particularly takes place in highmetal oxide component concentrations. The concentration of the metaloxide component is more particularly in a range above 35% and can extendto 60%. It is more particularly in the range 40 to 50%. Porous inorganicstructures are then produced, within which the polymer component isinterpenetrated by the metal oxide network.

[0047] The materials according to the invention have a thermal stabilityextending at least into the range 90 to 160° C. and can also cover thetemperature range 120 to 175° C.

[0048] During co-condensation, the production of a membrane can comprisethe formation of a mixture of ionic polymer and silica precursors in acommon solvent and the formation of a membrane from said mixture bypouring, casting or extrusion. The solvent can then be evaporated atambient temperature or by heating to temperatures up to 90° C. Thispermits the easy creation of membranes, even large membranes.

[0049] Hybrid polymer materials according to the invention are hybridsbetween organic polymers and mineral oxides. These materials combinewithin the same composite material and in a complimentary manner theproperties of each of the components. One method for the manufacture ofsuch hybrid materials according to the invention consists of using asol-gel process for obtaining a dispersion between the organic polymerphase and the inorganic phase on a molecular or nanometric scale. Suchsol-gel processes permit the preparation of dispersed materialsresulting from the growth of oxo-metallic polymers in a solvent. Thereaction is generally subdivided into two stages: metal alkoxidehydrolysis leading to the creation of hydroxyl groups, followed by thepolycondensation of hydroxyl groups and alkoxy groups in order to form athree-dimensional network. A general diagram of such a process is givenin FIG. 1. This diagram illustrates the polymerization of a siliconalkoxide and can be used in the invention. In the case of a metal oxideother than silicon, such as titanium or zirconium, the hydrolysis andcondensation do not require a catalyst, as a result of the highreactivity of the alkoxide. However, in the case of a silicon alkoxideand as shown in FIG. 1, the sol-gel process is catalyzed in an acid orbasic medium. Within the scope of the invention silicon can besubstituted by Ti or Zr. In order to facilitate the understanding of theclaims use has been made of the term SiO₂. It is therefore possible toreplace the term SiO₂ in the text by “SiO₂ or TiO₂ or ZrO₂.”

[0050] Hereinafter, the implementation of the invention is alsorepresented with the aid of the following groups of examples.

1ST GROUP OF EXAMPLES s-PEEK-TEOS-APTMOS System

[0051] A hybrid material according to the invention can be as-PEEK-silica and can be obtained from the sulphonated PEEK polymer andfrom the precursors TEOS and APTMOS. Hydrolysis and acid catalyzedcondensation of TEOS and APTMOS takes place. These precursors, whereofAPTMOS has the dispersing function, are added to the polymer solution.The growth of silica particles, i.e. the polycondensation reaction,takes place within the solution. An example of the hybrid materialobtaining process is shown in FIG. 2. A 10 wt. % sulphonated PEEKsolution in N-methyl pyrrolidone (NMP) is prepared by solubilizing thepolymer at 130° C. under nitrogen, followed by filtration. TEOS andAPTMOS are dissolved in NMP and added to the polymer solution. Stirringof the mixture is maintained up to homogenization, followed by theaddition of the requisite quantities of water and 1 M hydrochloric acid,dissolved in NMP. The solution is then heated, accompanied by stirring,to 60° C. until a homogeneous solution is obtained and on the basis ofwhich the membrane is cast in accordance with the conventionalprocedure.

[0052] Within said preparation, it is possible to vary two parameters:

[0053] i. the silica weight percentage in the hybrid membrane and

[0054] ii. the precursor/dispersant (TEOS/APTMOS) weight ratio.

[0055]FIG. 3 gives the composition of several examples of hybrid polymermaterials described hereinafter. The samples corresponding to theseexamples are designated s-PEEK-TEAP x.y.z. with

[0056] i. x=wt. % SiO₂ (in the hypothesis of a complete conversion ofsilanes into silica) and

[0057] ii. y/z=the weight ratio between the precursor and the dispersant(TEOS/APTMOS).

[0058] The formation of membranes used for different characterizationscan take place by a conventional solution casting preparation. Thesolvent (NMP) can be evaporated in vacuo at a temperature ofapproximately 100° C. for 4 hours. The hybrid polymer material films arethen detached from their support by immersion in water. A treatment ofthe films by a dilute hydrochloric acid solution can then follow inorder to eliminate any trace of solvent. The membrane is then obtainedin its protonated form.

[0059] The cation exchange capacity of the s-PEEK-silica membranes canbe measured by acid-basic dosing. Samples in acid form are treated by asaturated NaCl solution at 90° C. and for 3 hours. The protons freedinto the sodium solution are dosed by titration using a 0.1 M NaOHsolution. The cation exchange capacity (cec) of the material, expressedin meq/g, is calculated as the number of dosed protons relative to thedehydrated s-PEEK-silica sample mass. FIG. 5 shows the cation exchangecapacity (cec) of the s-PEEK-TEAP membranes of the samples as a functionof the introduced APTMOS quantity. The cation exchange capacity of thehybrid membranes decreases linearly when the APTMOS quantity increases.

[0060] However, the values of FIG. 4 show that the experimental cationexchange capacity for all the samples slightly exceeds the calculatedcation exchange capacity. These results indicate that all the NH₂functions have not been protonated.

[0061] A thermogravimetric analysis of the sulphonated PEEK can becarried out using a heating gradient of 10° C./minute. Thermogravimetricanalysis can be used for determining the silica content of the samples.Prior to the analysis, the membranes are placed in an oven at 50° C. forone hour.

[0062]FIG. 6 shows the results of the thermogravimetric analysesobtained for samples of s-PEEK and s-PEEK-TEAP membranes.

[0063] The general configuration of the thermograms of the hybridmembranes is substantially the same as that of an unmodified s-PEEKmembrane. The first weight loss, which occurs between 20 and 100° C.,corresponds to sample dehydration. However, it can be seen that thehybrid membranes have a lower water loss than in the case of a purepolymer membrane. The second weight loss, which starts at around 250°C., corresponds to polymer desulphonation. The desulphonation of thehybrid membranes occurs significantly earlier than with the purepolymer. The decomposition of the polymer occurs at approximately 400°C., no matter which sample is involved.

[0064] The polymer combustion residue at 1200° C. makes it possible toevaluate the silica quantity contained in the hybrid membrane. In thehypothesis of a total conversion of the precursors, a theoretical silicacontent has been calculated. The compositions of the hybrid membranesbased on TEOS are compared in FIG. 7.

[0065] The electrical conductivity of the samples was measured and FIG.8 shows the conductivity values obtained at 20° C. and 100% relativehumidity.

[0066] In order to determine the evolution of the conduction propertiesof the s-PEEK-silica membranes with the temperature, the conductivitymeasurements at 20° C. were supplemented by conductivity measurements ata temperature varying between 20 and 100° C. for 100% relative humidity.FIG. 9 shows the evolution of conductivities as a function of thetemperature of the membranes of different samples.

[0067] In the studied temperature range, there is a virtually identicalconductivity behaviour of the hybrid membranes under the same conditionsas compared with s-PEEK prior to the introduction of the mineral filler.

[0068] The introduction of aminophenyl siloxane into the s-PEEK-TEAPmembranes establishes a link between the organic matrix and the silicanetwork via the ionic interaction between the SO₃ _(⁻) and the NH₃ _(⁺)groups. In order to evaluate the influence of this ionic crosslinking onthe mechanical properties of the s-PEEK-silica membranes, tensile testswere carried out. FIG. 10 is a table showing the values obtained withthe different samples of the hybrid system during the breaking loadtests.

[0069]FIG. 11 is a graph showing the variations of the breaking load ofhybrid membranes as a function of the silica content and the APTMOSquantity.

[0070] For a given silica content, the breaking loads of the hybridmembranes, including APTMOS, are between the two extreme breaking loadvalues for s-PEEK and APTMOS-free hybrid membranes. This evolutionreveals the influence of ionic crosslinking in hybrid membranes on themaintaining of the mechanical properties of the unmodified organicmatrix.

[0071] The maximum elongation values given in the table of FIG. 20confirm that the rigidity of the membrane increases when silica isintroduced. This phenomenon is accentuated by APTMOS introduction.

[0072] The influence of APTMOS on the dispersion of silica particles fors-PEEK-TEAP hybrid membranes was analyzed by transmission electronmicroscopy and is shown in FIG. 12. The micrograph of a membrane sectionis shown in FIG. 12(a) for a s-PEEK-TEAP membrane 20.100.0 and in FIG.12(b) for a s-PEEK-TEAP membrane 20.90.10. The two membranes have thesame silica weight content. With the same magnification (×10,000), it ispossible to see aggregates located in sample (a) without APTMOS, whereassample (b) prepared in the presence of APTMOS as the dispersant revealsno particle aggregation. In the second case there is consequently anetwork interpenetrated by silica and polymer fibres.

[0073] Under a higher magnification (×50,000) in FIG. 13, thes-PEEK-TEAP sample 20.90.10 has very small silica particles organized inaccordance with a 10 nm wide strip network. It can be seen that anincreasing content of APTMOS as the precursor in the sol-gel reactionleads to a reduction in the size of the silica particles.

2ND GROUP OF EXAMPLES Nanometric Size Silica Particles Having a Surfacewith a Basic Character

[0074] This second group of examples refers to systems involving atransfer of silica nanoparticles from a colloidal, aqueous solution to apolymer solution. The polymer solution is e.g. a solution in NMP. Silicaparticles in colloidal suspension are marketed under the name LUDOX® andLUDOX LS® by Du Pont de Nemours. Such silica particles in a colloidalsuspension have no internal surface and are not crystalline. They aredispersed in an alkaline medium and carry a negative charge. Thisnegative charge produces the repulsion between the particles andstabilizes the colloidal form.

[0075] The addition of LUDOX to the polymer solution is followed by theevaporation of the solvent having the lower boiling point. During theevaporation of the water, the silica particles are transferred from theaqueous phase to the organic phase, without aggregation. The obtainingof an optimum dispersion is aided by the presence of APTMOS. Therequisite quantities of LUDOX and APTMOS, to which NMP is added, areadded to the polymer solution with 10 wt. % s-PEEK in NMP. The solutionis stirred and heated up to the complete phase transfer and theobtaining of a homogeneous solution, from which the hybrid membrane willbe prepared.

[0076] Different samples of variable composition are describedhereinafter in connection with this example. The samples are designateds-PEEK-LUAP x.y.z., x being the weight percentage of silica contained inthe sample and y/z the ratio used between LUDOX and APTMOS. Thecompositions of the samples appear in FIG. 14.

[0077]FIG. 15 shows the results of the thermogravimetric analysis of theLUDOX-based s-PEEK-silica membranes. As for example 1, the compositemembranes have the same weight loss profile as the pure polymer.However, there is a lower water loss for the hybrid membranes. Between20 and 100° C., they lose between 2 and 3% water, as against 12% in thecase of the pure s-PEEK membrane. The loss of sulphonic groups starts ataround 230° C. for s-PEEK-TEAP samples. The decomposition temperature ofthe pure polymer is not modified in the case of hybrid membranes andoccurs at 400° C.

[0078] The experimental composition of the hybrid membranes wascalculated on the basis of a combustion residue constituted by silica.The composition of the s-PEEK-LUAP membranes appears in the table ofFIG. 16.

[0079] It can be seen that for these membranes, the cation exchangecapacity decreases linearly when there is an increase in the APTMOSquantity introduced (table of FIG. 17). The variation between theexperimental and calculated cation exchange capacity values shows thatthere has not been a total transfer of protons between the aminophenyland sulphone functions. The coexistence of the NH₃ _(⁺) proton donorgroup and the NH₂ proton acceptor group should favour proton conduction.FIG. 18 shows the cation exchange capacity as a function of theintroduced APTMOS quantity.

[0080] The behaviour of the electrical conductivity as a function oftemperature was described in example 1 and appears in FIG. 9.

[0081] The results of mechanical tests performed on these compositemembranes appear in the table of FIG. 19. There are identical evolutionswith regards to the breaking load and maximum elongation for LUDOX-basedmembranes as in example 1. The breaking load decreases with the silicacharge, but can be significantly restored when a small amount of APTMOSis introduced. Thus, there is a breaking load restored to 71% fors-PEEK-LUAP 10.90.10 and up to 90% for s-PEEK-LUAP 10.70.30. Theevolution of the breaking load with the silica charge and with theAPTMOS quantity is shown in the graph of FIG. 20, which reveals theinfluence of ionic crosslinking on the mechanical properties ofLUDOX-based hybrid membranes.

[0082] The influence of APTMOS introduction on the “morphology” of asection through a hybrid membrane obtained from LUDOX can be gatheredfrom FIGS. 21(a) and 21(b). FIG. 21(a) shows the result of transmissionelectron microscopy through a s-PEEK-LUAP 20.100.0 membrane and FIG.20(b) the same microscopy of a s-PEEK-LUAP 20.90.10 membrane. The twomicroscopies were performed with a magnification of ×10,000. Oncomparing the two drawings, it can be seen that the silica dispersion issignificantly improved by APTMOS introduction. Thus, particle aggregatescan be identified in the membrane not containing a dispersant, whereasthe sample containing APTMOS has a quasi-homogeneous dispersion, whereonly a few aggregates remain. On the basis of the microscopic studies ofthe membrane of variable APTMOS/LUDOX composition, it can be seen that as-PEEK-LUAP 10.80.20. sample gives a virtually perfectly homogeneoussilica dispersion. No aggregate remains and observation under amagnification of ×50,000 reveals individualized silica particles ofapproximately 10 nm. This particle size is in accordance with theparticle size indicated for the commercial LUDOX solution. Thus, it ispossible to carry out a transfer of particles without particleagglomeration for a LUDOX:APTMOS ratio of 80:20. A view under ×50,000magnification of s-PEEK-LUAP 10.80.20 appears in FIG. 22.

[0083] The performances of the composite membranes prepared from TEOSand LUDOX were evaluated. FIG. 23 gives the polarization curves recordedfor composite membranes containing 10% silica and for which the bestdispersion of the component in the organic matrix was observed. Thesemeasurements were performed for 50 μm thick membranes and for O₂ and H₂gas pressures of 3.6 bars. The gas humidification temperature is 90° C.The table of FIG. 24 gives the strength and conductivity values for thefuel cell membranes at 100° C.

3RD GROUP OF EXAMPLES Inorganic Porous Structure

[0084] The table of FIG. 25 shows the results obtained with large silicaand therefore metal oxide concentrations. Structures are obtained wherethere is a hybrid material with an inorganic substrate interpenetratedby the polymer. With silica contents above 25 wt. % and using solventswith a high dielectric constant, permitting a salvation of ion pairswith strong electrostatic interactions, the results of the table areobtained. Therefore they prevent the aggregation of ion pairs. Using NMP(N-methyl-pyrrolidone) or DMF (dimethyl formamide) with relativedielectric constants of 30.2 and 37.8 respectively, a phase separationcan be observed. Using solvents having an even higher dielectricconstant such as tetramethyl urea or DMSO (dimethyl sulphoxide) with adielectric constant of 48.9, the homogeneity of the dispersion of thesilica is greater. FIG. 25 shows the influence of the aminopropyltriethoxy silane level on the silica dispersion in the case of 60 wt. %silica. In each case the silica source is tetraethoxy silane (THEOS).The table shows the silica weight percentage and the result obtained inFIG. 25 reveals that transparent, flexible membranes are obtained from acertain region and with a decreasing number of amino functions. Opaque,mechanically strong membranes are obtained on entering the phaseseparation zone. Just below the threshold, hybrid systems haveelectrical conductivities equal to or only slightly below that of thesilica-free s-PEEK polymer (better than 10⁻² Scm⁻¹ with 100% relativehumidity at 25° C.)

[0085] The table of FIG. 25 also shows the product co-condensationformation conditions. The synthesis temperature is in the range 60 to80° C., but can also be at ambient temperature.

[0086]FIG. 26 is a transmission electron microscopic observation (TEM)showing morphological arrangements differing very greatly from theresults according to FIGS. 1 to 24 (examples I and II). The silica isillustrated by clear zones, the black background of the imagecorresponding to the intercalated, organic polymer zones. The size ofthe ranges is smaller than 5 nm. In the phase with a relatively lowAPTMOS content, microscopic, aligned silica grains are obtained. Aporous structure in the incipient stage and silica particles accompaniedby sulphonated PEEK can appear. These systems have a very highmechanical strength compared with membranes prepared with lower silicalevels. FIG. 26 shows such a shot.

[0087] In the case of transparent membrane observation, silica particlesare no longer observed, even under high magnification.

[0088] There is a mesoporous silica matrix interpenetrated bysulphonated PEEK. There is a homogeneous integration of organic andinorganic components. The silica and sulphonated PEEK networksinterpenetrate forming co-continuous ranges with similar dimensions, thesmallest dimension of said ranges being at a level below 4 nm. Thesilica is located in the hydrophilic regions of the polymer. Byanalyzing the system by calcining the polymer, a porous structureremains and constitutes a replica of the polymer structure characterizedby a nitrogen adsorption and desorption.

[0089]FIG. 27 shows the isotherms obtained with the BET method. Byanalysis of the isotherms it can be seen that the silica has a verylarge surface area of around 700 m²/g⁻¹. The shape of the isotherm istypical of a mesoporous solid with a narrow pore distribution in therange between 3.5 and 4 nm. This is in accordance with the transmissionelectron microscopic photographs. The volume of the pores of theabsorption and desorption spectra of the measurement make it possible toevaluate the size of the pores with a volume of 0.6 cm³ g⁻¹ and a porediameter of approximately 3.4 to 4.5 nm. The measurement shown was madewith a 50% silica content and with a membrane having a conductivity of2.10⁻² Scm⁻¹, identical to that of the pure sulphonated polymer.

1. Hybrid material comprising a polymer having acid groups, said hybridmaterial containing a metal oxide component having at least Me_(x)O_(y)per molecule, each molecule of the metal oxide component containing atleast one functional group permitting an interaction and a spatialrelationship with the acid groups of the polymer.
 2. Hybrid materialaccording to claim 1, characterized in that the hybrid material forms apolymer matrix.
 3. Hybrid material according to one of the precedingclaims, characterized in that the acid groups are sulphonic groups. 4.Material according to one of the preceding claims, characterized in thatthe acid polymer material is an organic polymer, particularly afluorine-free organic polymer.
 5. Hybrid material according to one ofthe preceding claims, characterized in that the acid polymer material isformed on the basis of at least one of the following materials:polyheterocyclic, polyaromatic, polysulphones and sulphonicpolyarylether ketones, e.g. sulphonated polyether ketones such as S-PEK,s-PEEK, s-PEEKK and s-PEKEKK.
 6. Hybrid material according to one of thepreceding claims, characterized in that the functional group of themetal oxide component has a basic character, preferably being a basicfunctional group.
 7. Hybrid material according to claim 6, characterizedin that the basic character is due to a group containing nitrogen,preferably an amine and more specifically derived from APTMOS.
 8. Hybridmaterial according to one of the preceding claims, characterized in thatthe metal oxide component is present in the form of at least dimeric andmore specifically polymeric network chains.
 9. Hybrid material accordingto one of the claims 1 to 8, characterized in that the metal oxidecomponent is formed from metal oxide particles having on their surface,at least locally, a functional group, preferably basic groups. 10.Hybrid material according to claim 9, characterized in that the diameterof the metal oxide particles is below 50 nm, preferably equal to orbelow 10 nm.
 11. Hybrid material according to one of the claims 8 or 9,characterized in that the metal oxide particles are coated with amonomeric thickness layer of molecules having a functional group,preferably with a basic character.
 12. Hybrid material according toclaim 11, characterized in that the functional group contains nitrogenand in particular amino group, such as e.g. derived from aminophenylsilane.
 13. Hybrid material according to one of the preceding claims,characterized in that the spatial relationship between an acid group ofthe polymer material and the metal oxide component is due to a stronginteraction, particularly an ionic interaction between the functionalgroup of said component and the sulphonate group of the polymer. 14.Hybrid material according to one of the preceding claims, characterizedin that the metal oxide content is between 1 and 35 wt. %, preferablybetween 6 and 10 wt. %.
 15. Hybrid material according to claim 1,characterized in that the hybrid material comprises an inorganicsubstrate interpenetrated by the polymer.
 16. Hybrid material accordingto claim 15, characterized in that the metal oxide content is between 30and 60 wt. %, preferably between 40 and 50 wt. %.
 17. Hybrid materialaccording to one of the claims 1, 15 or 16, characterized in that thehybrid material comprises a porous inorganic substrate interpenetratedby an ionic conductive polymer.
 18. Hybrid material according to one ofthe claims 15 to 17, characterized in that the inorganic substrate isthe product of a co-condensation of a metal tetraalkoxide and afunctionalized trialkoxy metal, the metal and the metal oxide preferablybeing silica and silane respectively.
 19. Hybrid material according toclaim 18, characterized in that co-condensation takes place in thepresence of an ionic polymer.
 20. Hybrid material according to claim 19,characterized in that the ionic polymer belongs to a family of ionicconductive polymers or aromatic or heterocyclic ionomers.
 21. Hybridmaterial according to claims 15 to 20, characterized in that the porousinorganic substrate is-the product of a co-condensation in a tetraalkoxysilane-trialkoxy silane polymer solution functionalized by basic organicgroups in the presence of an ionomer.
 22. Hybrid material according toclaim 21, characterized in that the ionic polymer is an ionomer chosenfrom within the group of sulphone, phosphorus or carboxyl ionomers, moreparticularly a sulphonated polyether ketone.
 23. Hybrid materialaccording to claims 21 to 23, characterized in that the basic organicgroups are chosen from among alkyl or acrylamino groups and are moreparticularly aminophenyl trialkoxy silane, such as aminophenyltrimethoxy silane (APTMOS).
 24. Hybrid material according to claims 21to 24, characterized in that the alkoxy groups are chosen from amongmembers of the methoxy, ethoxy and butoxy group.
 25. Hybrid materialaccording to claim 17 to 25, characterized in that the inorganicsubstrate is porous and comprises a microinfrastructure interpenetratedwith the ionic conductor.
 26. Hybrid material according to claim 26(sic), characterized in that the microinfrastructure are pores, the sizeof the pores preferably being between 1 and 10 nm, more particularlybetween 2 and 8 nm.
 27. Hybrid material according to one of thepreceding claims, characterized in that the metal oxide is an oxide ofZr or Ti and in particular an oxide of Si, more specifically SiO₂. 28.Hybrid material according to one of the preceding claims, characterizedin that it is dissolved in a polar and preferably aprotic solvent suchas N-methyl pyrrolidone (NMP), dimethyl sulphoxide (DMSO), tetramethylurea (TMU) or dimethyl ethylene urea (DMU).
 29. Hybrid materialaccording to one of the preceding claims, characterized in that thehybrid material is a membrane, preferably used for cationic transfer inan aqueous medium.
 30. Hybrid material according to claim 30 (sic),characterized in that it is in particular a fuel cell membrane.
 31. Fuelcell, characterized in that at least one membrane is formed from ahybrid material according to one of the claims 1 to
 30. 32. Fuel cellaccording to claim 31, characterized in that the fuel cell operates withmethanol and at a temperature above 100° C.
 33. Process for theproduction of a hybrid material according to one of the claims 1 to 30,characterized in that the polymer material having acid groups is mixedwith the metal oxide component and/or with precursors of the componentin the presence of at least one solvent, the metal oxide componentand/or at least one of its precursors having a functional grouppermitting an interaction with an acid group of the polymer material, sothat the interaction and/or formation of the metal oxide component takesplace in the immediate vicinity of the acid group.
 34. Process accordingto claim 33, characterized in that the polymer material is dissolved inat least one solvent, dissolving preferably taking place under an inertgas and preferably at a temperature of approximately 130° C.
 35. Processaccording to one of the claims 33 or 34, characterized in that the metaloxide component and/or its precursors are dissolved in at least onesolvent.
 36. Process according to one of the claims 33 to 35,characterized in that the precursors of the metal oxide component arejointly in a solution with at least one solvent.
 37. Process accordingto one of the claims 33 to 36, characterized in that a metal oxidecomponent suspension and/or precursor solution of said component isadded to an acid polymer material solution and the mixture ishomogenized.
 38. Process according to one of the claims 33 to 37,characterized in that the at least one solvent is an aprotic polarsolvent, e.g. more particularly N-methyl pyrrolidone (NMP).
 39. Processaccording to one of the claims 33 to 38, characterized in that thefixing and/or formation takes place in accordance with a sol-gelreaction, preferably in the presence of water and an acid catalyst, e.g.more particularly hydrochloric acid.
 40. Process according to one of theclaims 33 to 39, characterized in that use is made of a precursor of themetal oxide component having a basic group and preferably containingnitrogen and preferably being an amine group, the basic groupinteracting with an acid group of the polymer material.
 41. Processaccording to claim 40, characterized in that the precursor has afunctional group in the form of functionalized alkoxy silane (R′O)₃Sir″or (R′O)₂″, more specifically APTMOS.
 42. Process according to one ofthe claims 33 to 41, characterized in that a precursor of the componentis a metal alkoxide ((RO)_(x)M), more particularly TEOS.
 43. Processaccording to claim 42, characterized in that the weight ratio of themetal alkoxide precursor to the functionalized alkoxy silane is at least70:30 and is preferably between 80:20 and 95:5.
 44. Process according toone of the claims 33 to 43, characterized in that the metal oxidecomponent is a metal oxide particle, more especially SiO₂, havingfunctional groups on its surface and more particularly formed fromAPTMOS.
 45. Process according to claim 44, characterized in that theweight ratio between the metal oxide particles and the functionalizedalkoxy silane is above 60:40 and is preferably between 80:20 and 95:5.46. Process according to claims 33 to 45, permitting the transfer of theinorganic component from an aqueous solution to a polymer solution in anorganic solvent.
 47. Process according to one of the claims 33 to 46,characterized in that following the interaction with and/or formation ofthe metal oxide component, solvent extraction takes place.
 48. Processaccording to one of the claims 33 to 47, characterized in that prior tothe extraction of the solvent, a membrane is formed, more particularlyby the pouring of the mixture onto a support.
 49. Process according toone of the claims 33 to 37, characterized in that the membrane with itsporous support is produced by the co-condensation of silicontetraalkoxide and functionalized trialkoxy silane in an ionic,conductive polymer solution.
 50. Process according to claim 49,characterized in that the membrane is formed in the absence of animpregnation of the inorganic substrate by an ionic, conductive polymer.51. Process according to claim 50, characterized in that the ionic,conductive polymer belongs to one of the families of ionic conductivepolymers, aromatic ionomers, or heterocyclic ionomers and is moreparticularly a sulphone, phosphorus or carboxyl ionomer.
 52. Processaccording to claim 51, characterized in that the ionic, conductivepolymer is chosen from within the group of sulphone, phosphorus orcarboxyl ionomers and is more particularly a member of the family ofsulphonated polyether ketones.
 53. Process according to claims 49 to 52,characterized in that co-condensation takes place in an aprotic solventwith a high dielectric constant.
 54. Process according to claim 53,characterized in that the relative dielectric constant is at least inexcess of 37 and preferably in excess of 45.